Pellicles are used to protect masks (also called reticles) from particles to reduce errors in transferring a pattern from the mask to a wafer. Pellicles include a frame which attaches to the mask; and a membrane extending across the frame. In some approaches the frame is secured to the mask using an adhesive.
In some approaches, the pellicle remains on the mask during a photolithography process. Light that passes through the membrane when a pellicle remains on the mask during the photolithography process has a reduced intensity due to absorption and scattering of the light incident on the membrane. In some approaches, the pellicle is removed from the mask prior to the photolithography process, such as an extreme ultraviolet (EUV) photolithography process. A cleaning process is used to remove adhesive used to secure the frame to the mask.